According to the ideas of exploration and the reservoir accumulation characteristics of shale gas，we have collected shale gas data in Ziliujing Formation from a batch of exploratory wells in Yuanba area of Sichuan basin. And industrial gas flow has been discovered in three wells of the exploratory wells. Research shows that Ziliujing Formation in Yuanba area is formed in shallow lake-semi-deep lake environment. Thick dark shale，high content of organic carbon and moderate thermal maturity of organic matter which is at the peak of gas production are developed in Ziliujing Formation. Moreover，quartz content is generally more than 60% in the mineral composition of shale, while clay content is below 30%. Gas content is high in shale of Ziliujing Formation, which is the basic condition for the formation and exploration of shale gas. And Ziliujing Formation is the favorable strata for the shale gas exploration.
Shale gas mostly develops in shale of high TOC forming reservoir “in place”. These top quality shale mostly grow in shelf facies and marine\|continental transitional facies in passive margin basin, intracratonic basin and foreland basin. The exploration of shale gas is different from the conventional oil and gas. This paper discusses the model for selecting shale gas region mainly by basin types and organic facies. The favorable target is controlled by TOC, organic matter maturity, the thickness and deepness of shale. The brittleness of shale，stratum subsidence history, temperature and pressure of the stratum and gas content in place etc constraint the location of “favorable target”, On the basis of the understanding about lower Cambrian strata in middle and upper Yangtze, it is concluded that western Hunan and Hubei Beidafang tectonic province in north\|west of Guizhou and the area of Weiyuan is the he most favorable exploration area.
Coal-bearing series,which expel bulk of organic acid during early burial stages is the base of deep basin gas accumulation. Organic acid would dissolve aluminum silicate minerals and cause rocks loosen and easy to be compacted. Furthermore,with the increasing of temperature,organic complex with Al3+ and Si2+ in from formation water decomposes into silica sediments causing high density of regional coal series sandstones. With the increasing of buried depth from late Jurassic to early Cretaceous,accompanied with the thermal event and the conversion procedure from lean coal to anthracite,mass gas gradually diluted,diffused,and dissolved formation water,and ultimately froming deep basin gas accumulation. Disproportion ablation and the formation of the massive southwestward monocline from late Cretaceous to Palaeocene Epoch caused the shallow buried depth of Permian coal series and the geothermal gradient decline. Deep basin gas borderline decreases because of the dissipation of bulk gas. Water vapour in “gas bin” recondensated to water and condensate water,named “acid point”,which present gas/water inversion and abnormal pressure features.
For knowing the distribution Pattern of Source\|Contacting Gas Accumulation for the Es3 in the Easten Sag of Liaohe depression, based on analyses of gas fundamental accumulation conditions, the existence of source-contacting gas is proved mainly by log and well log data.Combined with an analysis of source rock and reservoir, the paper also discusses the distribution of total gas curve, burial depth and thickness, and predicts the potential development area. It is indicated that total gas curve, burial depth and thickness are larger in the south and north of eastern sag and smaller in the middle. Niuju, Ciyutuo and Huangjindai in the north and Dapingfang, Rongxingtun in the Sorth are potential development area.
Normal hydrocarbon gas and CO2 coexist widely and a number of gas reservoirs with large volumes of carbon dioxide have been discovered in Songliao basin. Carbon dioxide can be sourced from inorganic, organic and mixed origins, in which the inorganic origin is dominated. Based on comprehensive analysis of carbon dioxide natural gas and regional geology, gas source of carbon dioxide and its degassing model are discussed. Study reveals that carbon dioxide in Songliao basin can be from mantle-derived magma, volcanic rocks, carbonate rocks and organic matters. Mantle-derived magma in crystalline basement, especially Cenozoic alkali basaltic magma, is the most significant gas source. Volcanic rocks in sedimentary cover are another significant gas source, and medium-acidic volcanic rocks of Yingcheng and Denglouku Formations could be principal gas source in east Changde gas pool. Carbonic-Permian carbonate rocks in metamorphic basement need more attention to study as gas source in future exploration. There are abundant organic matters in sedimentary cover and metamorphic basement, but its contribution to form large volumes of carbon dioxide accumulations is little. Degassing models varies with different gas sources. There are four types of degassing models for mantle-derived carbon dioxide to migrate into basins, including direct degassing through lithospheric faults from the upper mantle, degassing from mantle diapir bodies, degassing through low\|velocity and high\|conduction zones as intermediate repeater and basement faults, and after-releasing of absorbed gases by volcanic rocks. Degassing of carbonate rocks in contact and dynamic metamorphisms is favorable for carbon dioxide accumulations.
Xujiahe Formation in Sichuan basin, developed three sets of mudstone source rocks and dense sandstone reservoirs, which are interbedded and distributed in a large area. By analyzing the known typical gas reservoirs, it is clearly that gas migration as well as accumulation occurred near its source rock, and the gas reservoirs′ distribution are greatly separated horizontally, which are controlled by the efficient source reservoir combinations. Careful statistics research was carried out to the sand and mud combination distributed in the T3x3 source rock and T3x4 reservoir rock, and the efficient source\|reservoir combinations not only develop between the T3x3 and T3x4, but also are inside the T3x3 and T3x4 itself. The source rock quality, gas generation intensity, reservoir properties and efficient thickness of source\|reservoir combinations in T3x, decide its efficiency to the gas accumulation and gas reservoirs distribution horizontally.
Reservoirs of the upper Triassic Xujiahe Formation has characteristics of low compositional maturity, low cement content and medium maturity in Sichuan analogous foreland basin. Lithology is regularly distributed in plane, dominated by lithic sandstone in the northwest region. lithic sandstone and feldspathic sandstone mixed in central west region, lithic feldspathic sandstones in southwest region, feldspathic lithic and lithic quartz sandstone mixed in central-south region. Reservoir has poor physical properties in general, which are mainly low porosity and permeability reservoir. Only a few reservoirs with middle porosity and low permeability develop in some regions. Because of the sedimentation, diagenesis and tectonic difference in thrust belt, foredeep depression zone, foreland slope and foreland uplift, of the reservoir porosity has zoning characteristics. Reservoir space in Longmen Mountain thrust belt are mainly fracture with small amount of emposieu and original intergranular pore. The pore type in foredeep depression zone is fracture-secondary dissolved pore, dominated by secondary dissolved pore with little primary pore. In foreland slope, the pore type is mainly secondary dissolved pore and primary pore. While in foreland uplift, the pore is mainly dissolved pore and primary pore. The development of reservoirs is controlled by deposition, diagenesis and tectonic disruption.
The Ordovician carbonate suffers from multi-stage and multi-type paleo\|karst in south of Ordos basin. The development of paleo-karst is controlled by ancient tectonic setting, lithologic association characteristics, and especially ancient geology and landform. On the basis of field mapping method, impression method, residual thickness method, and according to the result of seismic facies trace and seismic interpretation, the paper depicts ancient geology and ancient landform in detail in south of Ordos basin. From south to north, ancient landform is divided into karst highland, karst platform and eroded slope. The eroded slope is furthermore divided into the erosion shallow grooves, erosion pits, karst hills and karst beams. Due to the different paleo\|karst background and paleohydrologic conditions, the distribution of favorable areas is obviously different.
The Mesozoic reservoirs in Zhenjing oilfield is characterized by tight reservoirs, low permeability, low abundance and large reserves. It has favorable exploration potential which is shown by the drilled high-yielding wells. Previous studies indicate that there are multiple dynamic systems for hydrocarbon migration and accumulation in the southwestern Ordos basin. And different systems have different dynamic and carrier path for secondary migration. Through the research on buried history, mudstone compaction curve and physical property of reservoirs, it is concluded that the dynamic of secondary migration in Chang8 Member with ultra-low permeable reservoir is overlying abnormal pressure but Yan'an reservoir is buoyancy. Besides, hydrocarbon in Chang6 Member reservoir which is characterized by low permeability accumulated through underlying abnormal pressure mainly and buoyancy locally. Furthermore, permeable bed is the chief carried path in Chang8 Member, while fracture becomes the primary path in Chang6 Member. Permeable bed is the subordinate way for Chang6 Member reserviors. As for Yan'an Formation, various channels including fracture, unconformity and permeable bed could carry hydrocarbon. From the study on dynamic and carrier path of secondary migration, tracking the hydrocarbon movement can become more accurate and exploratory theories for further exploration.
Because of the multicycle, unbalance of tectonic movement and sedimentary evolution, the reservoir forming and distribution is very complicate.In the past few years, with the growing knowledge of Tarim basin, it is necessary to strengthen the study of reservoir forming regularity.On the basis of proved reservoir forming characteristic, the reservoir forming pattern can be divided into seven types, including anticline gas reservoir from foreland subsalt compaction, structure-lithologic irreducible reservoir in foreland upsalt, structure-lithologic reservoir in foreland platform-basin folding area, carbonate weathered crust in platform-basin palaeohigh, interstratal karst stereoscopic combined reservoir in carbonate weathered crust, clastic combined reservoir in platform\|basin palaeohigh, structure-lithologic reservoir inplatform-basin long-term palaeoslope reverse, structure-lithologic irreducible reservoir in platform-basin long term bulge deep layer.Through analysis of the reservoir forming pattern and distribution regularity in different structure area and structure layer, the paper point outs that Kuche depression, Tabei uplift and Tazhong uplift are the three main fields for increasing reserves and production.In addition, Taxinan depression, west Qiulitage, Silurian to Triassic Formation in the platform-basin area of Tarim basin and low bulge in the east of Tarim basin are the important target for further exploration.
Based on comprehensive analysis of field section, drilling well data, well core, and the detailed stratigraphic division and correlation, combining with the seismic interpretation data，the Bachu Formation was divided into four lithologic members, and four depositional systems identified, which are littoral depositional system, carbonate platform depositional system, shelf depositional system and fan delta depositional system. Combining with the tectonic setting and the characteristics of sea-level change, the lithofacies palaeogeography of Bachu Formation was divided into four evolution stages. The stage of initial transgressive with shelf deposition in the western and tidal flat deposition in the central part of Tarim basin, the stage of maximum marine flooding with open platform deposition in the western and restricted platform deposition in the central part of Tarim basin, the stage of slow decline in sea level with evaporation platform deposition in the western and tidal flat deposition in the central part of Tarim basin, the stage of rapid transgression with open platform deposition in the western and restricted platform deposition in the central part of Tarim basin. In the early Carboniferous period, the northern, eastern and south\|central part of Tarim basin in the uplift and erosion, and provide a stable source for sedimentation.
The North-Kunlun faults zone is a slope zone which is formed and developed in Cenozoic Era, and it has the features of different zones in north and south, different parts in east and west, and different formations above and below formation, and it effects this area so much that the local structures have quite different reservoir forming conditions in different parts. The hydrocarbon exploration mostly consider some structural unit as the basic research target because they have closer basement, structural, deposit characteristics and similar controlling factors of reservoir\|formation, thus it is favorable to guide the exploration direction and deployment on the basis of the division of structural unit. So, based on seismic, drilling, and logging data, and according to the rolling shape of basement structure, faults distribution and their combination characteristics, the North-Kunlun faults zone can be divided into six structural sub\|units , which are: west slope belt, central folding belt, north folding belt, east folding belt, Dongchaishan folding belt and north slope belt. By investigating their geological background and faults combination, and the prospect evaluation is also carried out, which indicates that the west slope zone is the more favorable area for present hydrocarbon exploration, the north slope belt is the favorable exploration succeed area. Thus, the conclusion will be helpful for the research of hydrocarbon formation and further hydrocarbon exploration in North-Kunlun area.
The large-scale gasfield, containing many gas reservoir layers mainly composed of Carboniferous volcanic rocks, is discovered in the Dinan uplift-the south of Dishuiquan depression in central Junggar basin. Dibei uplift, near the Dishuiquan depression in south and Wulungu depression in north, is considered as the favorable region of hydrocarbon accumulaion from two depressions. Recently, small-scale gas reservoirs have been found in Jurassic and Carboniferous strata, but no greater breakthrough has been made. It is still unclear about the origin of the natural gas of the Dibei uplift. By comparing with carbon isotope of natural gas and reservoir extraction of gas intervals, it is showed that the geochemical characteristics of natural gas in Dibei and Dinan uplift has significant differences, and natural gas of Dibei uplift is similar with that from typical Carboniferous sources in the eastern part of the basin. Consequently, the natural gas should be sourced from Wulungu depression whose geochemical characteristics of rocks in Carboniferous are similar with Dibei uplift. Based on the characteristics of fluid inclusions, it is concluded that the gas is accumulated at late stage of late Cretaceous.
Kunteyi depression is located in western fault block of northwestern Qaidam basin, near the Lenghu structure zone and Eboliang structure zone. It is one of the most important potential areas of oil and gas exploration in northwestern Qaidam basin. By analyzing the Mesozoic and Cenozoic stratigraphic characteristics and geological interpretation of seismic data，the paper comes to conclusion that the prototype basin of Kunteyi depression was extrusion\|type and intersected block depression in Mesozoic because of a large number of intersected block in depression. With Himalayan tectonic movement and Altyn Tagh fault activities, Qaidam basin was in the pressure\|shear stress field in Cenozoic. Kunteyi depression was also in the pressure-shear stress field and developed into extrusion\|type depression in Cenozoic. With the Altyn Tagh fault activities，Kunteyi depression was in the pressure\|shear stress field in Cenozoic. The deep structural belt began to develop in early Cenozoic and formed in Quaternary.
The Cretaceous-Tertiary clastic gas reservoir with rich gas condensate in southern Tianshan area of the Tarim basin displays low\|resistivity property. The value of gas resistance of Suweiyi Formation，Kumugeliemu Group of the lower Tertiary and Bashijike Formation of the lower Cretaceous, ranges from 1 to 3 Ω·m, and that of Yageliemu Formation of the lower Cretaceous varies from 4 to 9 Ω·m. The electrical property of gas reservior has the following features: ①Similar to or a little higher than that of water layer; ②Lower than that of surrounding rock ;③Generally higher than that of fomation zone, with the characteristic of RFOC＞RILM＞RILD in the three-resistivity\|curve. According to the analysis of drilling, logging and well test data, it is found that the lithofacies, lithology and fluid characteristics of reservoir provides favorable geology condition, while high irreducible water saturation and high formation water salinity is the main reason for the formation of the low resistivity gas reservoir, but high formation temperature may reduces the resistivity.
For lack of drilling data in Gucheng area, study of carbonate platform has been carried out based on seismic facies assemblage analysis method, combined with sedimentary facies analysis of single drill and geological data. Platform has experienced three evolution stages, including slope, feeble edging carbonate platform and edging carbonate platform. From early Cambrian to early-middle Ordovician, the width of slope becomes narrower gradually, while platform edge becomes wider, with dome shape external edge. By the end of middle Ordovician, platform has been evolved with relative high energy. Analysis of planar seismic facies indicates that each facies is not distributed regularly in evolution process. The Gucheng carbonate platform evolves gradually, which was completely different from Tazhong carbonate platform. Carbonate builtup in platform edge is mainly composed of mud mound. The grains are well cemented and framework reef is not developed.
Fluid inclusion in reservoir implies abundant information of reservoir-forming, which is widely used in research of thermal history, reservoir\|forming, and more territories in petroliferous basin. It is revealed that homogenization temperature of fluid inclusion in oiliness reservoir is more than its normal burial temperature. Reservoir calculated in view of the above is usually formed in late stage with relative high fluid paleopressure. Hydrocarbon-bearing fluid inclusions are mainly trapped in the early and middle period of petroleum migration and accumulation. The maturity of organic material is ordinarily lower than that of crude oil in reservoir. It is difficult to form abundant hydrocarbon-bearing fluid inclusions in the early stage of a little petroleum migration and in late period of a great quantity of petroleum migration speedily. Paleo-OWC and reservoir-forming stages assured by abundance of fluid inclusion are less. The hypothermal fluid action in the late evolution period is favourable for the migration and accumulation of adsorbed hydrocarbon in migration pathway. The results have great significance to study formation mechanisim of fluid inclusion and reservoir.
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When the rock is deformed by pressure decreasing in the formation, it is difficult to study the non-linear elasticity deformation rock volumetric strain.According to the power relationship between the non\|elastic deformation rock elastic modelling quantity and effective pressure, this paper establishes the theoretic expressions between rock volumetric strain and effective pressure under the surface experiment conditions and the formation conditions, proposese a new method of the “Trial Calculation & Iteration”used to study the non-linear elasticity deformation rock volumetric strain quantitatively, calculates the a and b values of the rock non\|linear elasticity deformation constants by means of the experiment data between the non-linear elasticity rock volumetric strain and the effective pressure, and forecastes the non-linear elasticity deformation rock volumetric strain quantitatively.The application of this method indicates that the relative errors between the predictive values of the non-linear rock volumetric strain, rock porosity under the surface experiment conditions ＆ rock porosity of the formation pressure decrease and the experiment values or the predictive values using experiment data of them should be less than or equal to 7.39%, 0.80% & 3.92% and preferable consistance, and that it is possible to convert from the experimental data of the surface conditions to the data of reservoir conditions.This method provides an effective way to calculate the non-linear elasticity deformation rock volumetric strain quantitatively.
Extensive investigation on geochemical characteristics,origin and source of H2S-rich natural gas in the northeastern Sichuan basin was processed and abundant documentation was accumulated in resent years.But a great attention has been paid and controversy existed all along on the origin and source of the natural gas in the northeastern Sichuan basin because of the specific geological environment and the complicated condition of natural gas formation and evolvement of the area.The correlations between the content of hydrogen sulphide and the components of hydrocarbons,the carbon isotopic compositions of methane,ethane and carbon dioxide indicate that the H2S-rich natural gases reservoired in the Feixianguan and Changxing Formations of the northeastern Sichuan basin are the product of oil cracking under the catalysis of sulphate and possibly derived from the Silurian source rocks;and that the generation of 13C-riched CO2 in the H2S-rich natural gas is related to the reduce of H2Scontent in natural gas and is the result of H2S corrosion on reservoir carbonate.
By taking pyrolysis experiments in closed and open systems,the relationship and evolution of hydrocarbon products for Nanning lignite have been studied.The results show that in the closed system,the temperature range that liquid hydrocarbon exists is from 250℃ to 600℃,and it is from 250℃ to 550℃ for the open system.By comparing production rate of hydrogen,gaseous hydrocarbons and liquid hydrocarbon,we discovered that liquid hydrocarbon is the major factor affecting polycondensation of organic matter.In the two systems,there is a negative correlation between the production rate of hydrogen and liquid hydrocarbon,gaseous hydrocarbons and liquid hydrocarbon.But the production rate of hydrogen and gaseous hydrocarbons has a positive correlation.This shows that organic evolution is a stable process affected by the bond energy of chemical bonds and not related with experimental methods and processes.In the high temperature stage,the production rate of gaseous hydrocarbons is almost equal under the open and closed systems.Therefore,when calculating the gas volume,the evolution degree should be taken into account in choosing gas production rate.
Western South China Sea is the main exploration and development field for CNOOC with great exploration potential. In nearly 40 years of exploration, it has experienced multi\|level, multi\|field, multi\|zone, and multi-objective exploration from shallow shelf to deep water. In recent years, with the increasing of exploration intensity in deep formation, we have made great breakthrough in geophysical exploration， seismic data acquisition and processing technology. According to geological features and the characteristic of the geophysical information in different basins of South China Sea , the paper proposes to make good use of traditional seismic data processing techniques and methodologies. At the same time, for the new problem in new field of complex geological conditions, we should create new seismic data processing techniques and methods constantly, form a series of ripe seismic data processing technology gradually, and provide technical support for oil and gas exploration in northern South China Sea setting up “Daqing Oilfield at the Sea”.
The coal measure source rock in Y Formation is one of the important source rocks in X sag, the distribution of which is critical in assessing exploration prospect of X sag. Based on previous work, our study aimed at principal problems to analyze the petrophysical characteristics of the coal bed. The logging series that could be used to separate the coal bed from the wall rock was defined with forward modeling. The geophysical response of coal measure was analyzed by combining with seismic attribute analysis. In addition, the geological characteristics of the coal measure was recognized through the geophysics characteristics by integrating the core, well log, geochemical and palaeontology data to analyze the coal forming environment in the sag and the distribution of coal measure. The northwest of X sag is believed as the favorable areas that developed the coal measure in Y Formation and rich in coals. The analysis technique of seismic attribute represented by multiple-attribute regression is suitable for the prediction of the coal measure distribution.
Reservoir of He-8 Member in SU X well block of Sulige gas field has strong heterogeneity，and conventional prediction methods is not satisfactory. Therefore，in order to identify sand body and predict gas bearing block in the research area, prestack and poststack reservoir prediction methods were used in the paper. Firstly, seismic attributes analysis and lithologic stochastic inversion were comprehensively used for sand body identification. On the basis of identification result and the analysis of the sedimentary characteristics, the distribution law of sedimentary microfacies of He-8 Member in the research area has been determined. Secondly, by comprehensively utilizing the results of seismic wavelet absorption coefficient analysis, AVO analysis and pre-stack elastic inversion, gas bearing potential for anomalies was interpreted on the section. Finally, combined with sedimentary microfacies distribution characteristic of He-8 Member and gas bearing analysis results，gas bearing block was synthetically evaluated. Drilling result shows that the multiple prediction method is good, complementing the disadvantages of each other, reducing the uncertainty of prediction results and providing a reliable basis for further development and deployment.
Hydraulic fracturing is generally applied to improve productivity for the low permeability of the coal seams in China. Fracture fluid has a serious leakoff for considerable nature fractures of coal and can not effectively flow back for strong adsorption capability of coal. The result of these performance leads to permeability impairment and reducing effectiveness of stimulation treatment. This paper studies characteristics and effective stress affecting of coal spontaneous imbibition through water imbibition experiment. The results show that imbibition rate will increase with permeability increasing. Spontaneous imbibition curves can be divided into tow parts of spontaneous imbibition and diffusion\|adsorption. Imbibition rate will decrease nearly one order of magnitude considering effective stress. It indicates that permeability and effective stress are factors affecting water spontaneous imbibition. The paper points out that capillary pressure and attractions between water molecules and coal molecules determines the characteristics of water spontaneous imbibition by analyzing adsorption mechanism and pore structure. The conclusion has some reference significance for evaluation of aqueous phase trapping, optimization of hydraulic fracturing method and fracture fluid design.
It is normal to see that some water occurs in low permeability gas reservoir which influences the gas supply ability. The paper builds a model according to the pore structure, studies the occurrence models of water in different pores and the mechanism that influences the gas flows. The paper also studies the water breakthrough condition in the gas reservoir and the influence to the gas supply ability by physical simulation method. The result shows that there are two types of water in pores, movable water and residual water, which are both determined by reservoir physical properties and gas drive pressure. Movable water mainly occurrs in the fracture and big pores, and the residual water has many occurrence models in differential pores. The result also shows that when the water body is bigger than 6.0PV in gas reservoir, it′s easy to break into the formation. After wetting, some water is remained in the pore just as residual water occupying part or whole flow path. This will make the reserves far from the well and difficult to be employed, so it will influence development of the low permeability gas reservoir.
Low-permeability reservoir has been paid more attention to in exploration and development as conventional reserve decreases, while economical development and management for low\|permeability reservoir are severely restricted by stress-sensitivity. A summary about previous on stress-sensitivity was made from evaluation method, fluid-solid coupling model and deliverability equation. It is indicated through analyzing that method based on in-situ stress compound with multinomial equation has a desirable accuracy in stress-sensitivity assessment; Development of numerical simulation softwares with regard to fluid-solid coupling and deliverability equation and water injectivity prediction will be the research priorities in this field. It is also pointed out that in no way can stress-sensitive mechanism be revealed merely based on phenomenology or theoretical derivation. It's proposed that a comprehensive evaluation system should be obtained taking into account experimental data, theoretical formula and reservoir characteristic; Establishing appropriate structural model of fracture plane and computer simulation method considering interaction between fracture network comprised of natural and hydraulic fractures is the choke point for fracture stress-sensitivity yet to be broken.
On the basis of studying the reasons of oil wells′ water rise rapidly in the second area of Dalugou and Baiyushan area of Jing′an oilfield, the paper studies the expansion characteristics, stability, and profiles improve ability in different environment of the “Water Flowing Direction Changing Agent” and “Associated Polymer”, which are the main components of the “pre-cross linked particle + PL profile control agent + Associating Polymer + Water flooding the flow of change agent” profile control system. This profile control system is used in field experiments too. The application and evaluation show that the system can effectively block permeability path and make deep flow shifted. It also has characteristics of long valid period, simple construction process and little environmental pollution. The systems can solve the problems of the reservoirs′ well-water rise fast (or flooding) and low recovery in second area of Dalugou and Baiyushan area, and provide technical support for the management of large pores or cracks reservoirs which produce water.
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